A number of small bandgap or semimetallic transition metal chalcogenide (TMC) compounds have recently attracted interest as promising excitonic insulator candidates [numbers[1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]}, [9]}]. The reduced dimensionality of TMCs results in weak screening of the Coulomb interaction and consequently large exciton binding energies, which could lead to condensation at non-cryogenic temperatures.
Among this family of materials, particular attention has been devoted to Ta\(_2\) NiSe\(_5\)  following hints of the potential existence of an EI phase below 328 K. [numbers[3]}, [4]}, [5]}, [7]}, [8]}, [9]}, [16]}, [17]}, [18]}, [19]}, [20]}, [21]}, [22]}, [23]}]. These works have provided insights into the properties in Ta\(_2\) NiSe\(_5\) , for instance, by using equilibrium [numbers[3]}, [7]}] and time-resolved [numbers[4]}, [27]}, [19]}, [18]}, [22]}] angle-resolved photoemission spectroscopy (ARPES), by analyzing the effect of physical and chemical pressure [numbers[9]}, [23]}], doping [numbers[17]}], and by detecting anomalies in charge transport [numbers[9]}], optical signatures [numbers[35]}, [36]}] and phonon properties [numbers[5]}, [16]}, [20]}, [21]}, [23]}, [42]}] as a function of temperature.
